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# Physics Coursework, Errors and Uncertainties watch

1. If anyone knows about percentage errors and uncertainties please, if they are willing, pm me as I have a mound of errors to work out in a piece of coursework which I can't seem to find out how through the textbook.

My question is, if my mean reaction time with a stopwatch is 0.30 s +/- 0.005 s (due to the stopwatch being to 2 d.p,) is the uncertainty in the time taken for an object to fall, measured with the same stopwatch, my reaction time plus the stopwatch uncertainty (0.30 + 0.005 = 0.305) or should the uncertainty also include the additional stopwatch uncertainty of timing my reaction time (0.30 + 0.005 + 0.005 = 0.31)?
2. If your reaction time is estimated at 0.3s and you press the watch button twice to time something, then the maximum error (possible error) is 0.6s
There is no need to consider the precision of the scale on the watch is this is very small in comparison.
The probable error will be smaller than 0.6s
If you take repeated measurements of the time and find the mean value, this will reduce the error.
3. (Original post by Stonebridge)
If your reaction time is estimated at 0.3s and you press the watch button twice to time something, then the maximum error (possible error) is 0.6s
There is no need to consider the precision of the scale on the watch is this is very small in comparison.
The probable error will be smaller than 0.6s
If you take repeated measurements of the time and find the mean value, this will reduce the error.
The object began its decent the moment the stopwatch was started, they were hooked up in a mechanical system which allowed the time difference between starting the watch and the object descending to be negligible.

I am in no way trying to offend you, however my teacher has told me that the small 0.005 s uncertainty in the stopwatch must be accounted for. I hate this coursework
4. (Original post by Pythag)
The object began its decent the moment the stopwatch was started, they were hooked up in a mechanical system which allowed the time difference between starting the watch and the object descending to be negligible.

I am in no way trying to offend you, however my teacher has told me that the small 0.005 s uncertainty in the stopwatch must be accounted for. I hate this coursework
If you hooked up the watch to a system that didn't involve your reaction time then clearly you don't need to consider reaction time. If you stopped the watch manually at the end then you only need to consider the reaction time once.

Your teacher is right that it needs to be "accounted for". The point here is how it is accounted for and why.
If you know there is an uncertainty of ±0.3s in the measurement due to reaction time, and the watch has a precision of ±0.005s, then this precision is very small compared to the reaction time error.
For the purpose of estimating the uncertainty in the total measurement and taking that through to a final result, it is insignificant and would not be included.
It is frankly ridiculous to quote an uncertainty of ±0.305s when the 0.3s is a gross estimate.
What is important is that you know, and account for, the fact that the watch does have a precision, but that it is very small compared to the overall error.
I imagine that's what your teacher will tell you.
If not I will just have to disagree with him/her.
It's up to you who you believe.
5. Thank you.

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